The present invention concerns an air filter for use in a clean room used, for example, in factories or research laboratories relevant to the field of semiconductors, foodstuffs and biotechnology, a method of manufacturing thereof, a local facility and a clean room equipped with the air filter.
In clean rooms used heretofore, for example, in factories or research laboratories in the relevant field of semiconductors, foodstuffs, medicines and biotechnology, dry air filters for trapping air-born particles are disposed to air introduction paths and air passing there through is introduced into the clean room.
Air filters used at present in clean rooms include ULPA (abbreviation for Ultra Low Penetration Air) using glass fibers for the filter medium and HEPA (abbreviation for High Efficiency Particle Air), and such filters are excellent filters in view of removal of dusts and, for example, ULPA filters can remove fine particles even of 0.1 xcexcm. Further, non-glass type filters using fluoro resin or quartz fibers instead of the glass fibers for the filter medium have also been developed so as not to release inorganic substances from the air filters.
Recently, with the increase of integration degree of semiconductors, diffusing of gaseous organic substances as well as dusts in the clean room air have considered to be the cause of defects. That is, it has been pointed out that organic substances are adsorbed on the surface of semiconductor substrates (silicon wafers) in clean rooms, to deteriorate device characteristics (for example, Fujii, xe2x80x9cGaseous Contaminants and Current Situation for Countermeasure of Removalxe2x80x9d, Air Cleaning, Vol. 32, No. 3, p 43 (1994), published from the Foundation of Japan Air Cleaning Society).
Further, it has been well-known that an n-type semiconductor is obtained by doping P (phosphorus) and a p-type semiconductor is obtained by doping B (boron, into a silicon wafer in semiconductor manufacturing steps but, if phosphorus compounds or boron compounds are present in the clean room air, these may possibly cause unnecessary doping, so that it is necessary to remove such ingredients from the clean room air.
The present invention has been accomplished to solve the problems described above and it is an object thereof to provide an air filter for trapping air-born particles that can eliminate the presence of gaseous organic substances, for example, in clean rooms, semiconductor production apparatus or the like, a method of manufacturing an air filter therefor, a treatment agent constituting the air filter, a method of manufacturing a filter medium, a clean room and a local facility such as a semiconductor production apparatus in which gaseous organic substances are not present, as well as a clean room and a local facility in which phosphorus compounds and boron compounds are not present.
The present inventors have made earnest studies for attaining the foregoing object and, as a result, have accomplished the present invention based on the finding that presence of gaseous organic substances in a clean room and a local facility such as a semiconductor production apparatus is mainly caused by air filters disposed to air introduction paths and gaskets intervened for attaching the air filters to openings, for example, of a ceiling.
That is, it has been found by the study of the present inventors that gaseous organic substances such as cyclosiloxanes, carboxylic acid esters, phosphoric acid esters, hydrocarbons, and phenols are released from the existent air filters described above and that such organic substances are released from treatment agents impregnated between each of fibers upon forming the fibers into a cloth-like filter medium (including a binder for binding fibers, a water repellent for improving dust trapping effect and a plasticizer or an antioxidant), silicone oils deposited to fibers in a case where the filter medium is glass fibers (this is a reinforcing material upon spinning glass fibers which serves also as a water repellent of the filter medium) and sealing materials for bonding a filter medium and a frame. Further, it has also been found that organic substances are detected at a high ratio also from rubber materials used so far as gaskets.
Specifically, it has been found that the ingredient of the conventional water repellent (non-silicone type) in the treatment agent is liquid paraffins (aliphatic hydrocarbon having 12 to 18 carbon atoms) which contain a plasticizer or an antioxidant of relatively low molecular weights Further, while the sealing material comprising a polyurethane or epoxy type resin as the main ingredient is used, it has been found that isocyanates of the main agent left after the curing reaction become organic contaminations in a case of a two component polyurethane resin, while amine compounds used as a curing agent become organic contaminations in a case of a two component epoxy resin. It has also been found that conventional sealing materials contain plasticizers and antioxidants of relatively low molecular weight.
Based on the findings described above, the present invention provides an air filter comprising a filter medium formed of fibers treated with a treatment agent into a cloth-like shape, a frame for containing the filter medium and a sealing material for tightly sealing a portion between the frame and the filter medium for trapping air-born particles, wherein at least one of the filter medium and the sealing material does not release gaseous organic substances during use.
Further, the present invention provides an air filter satisfying one of the following definitions (a)-(c) and (e)-(g) for the treatment agent and the sealing material.
(a) The main ingredient of a non-silicone type water repellent contained in the treatment agent is at least one of an aliphatic hydrocarbon having 20 carbon atoms or more and a higher alcohol having 18 carbon atoms or more.
(b) The main ingredient of the plasticizer contained in the treatment agent is at least one of carboxylic acid esters, polyester and epoxy type compound having 400 or more molecular weight.
(c) The main ingredient of the antioxidant contained in the treatment agent is a phenolic compound having 300 or more molecular weight.
(e) The main ingredient of the plasticizer contained in the sealing material is at least one of carboxylic acid esters, polyesters and epoxy type compounds having 400 or more molecular weight.
(f) The main ingredient of the antioxidant contained in the sealing material is a phenolic compound having 300 or more molecular weight.
(g) The main ingredient of the lubricant contained in the sealing material is at least one of an aliphatic hydrocarbon having 20 carbon atoms or more and a higher alcohol having 18 carbon atoms or more.
Further, the present invention provides a method of manufacturing an air filter which comprises selectively using the plasticizer and the antioxidant defined in (b), (c), (e) and (f) for the treatment agent and the sealing agent described above.
Now, if the main ingredient of the non-silicone type water repellent in (a) and the main ingredient of the lubricant in (g) are an aliphatic hydrocarbon having 19 carbon atoms or less and a higher alcohol having 17 carbon atoms or less, the gaseous substances are present in the clean room air being entrained by air passing through the air filter in a usual clean room, which is controlled at a temperature of 23xc2x0 C. and at a humidity of 30-40% and in which the flow rate of air passing through the air filter is about 0.3 to 0.4 m/s, but such gaseous substances are not present in the clean room air when an aliphatic hydrocarbon having 20 carbon atoms or more and a higher alcohol 18 having carbon atoms or more is used.
Further, if the main ingredient of the plasticizer in (b) and (e) is dibutyl phthalate (molecular weight 278), dioctyl phthalate (molecular weight 391) or di-2-ethylhexyl adipate (molecular weight 371) having 400 or more molecular weight, the gaseous substances are present in the clean room air being entrained by air passing through the air filter in the usual clean room, but the gaseous substances are not present in the clean room air if those having 400 or more molecular weight are used.
Further, if the main ingredient of the antioxidant in (c) and (f) is 2,6-di-t-butyl-p-cresol (molecular weight 220.4) having 300 or more molecular weight, the gaseous substances are present in the clean room air being entrained by air passing through the air filter in the usual clean room, but the gaseous substances are not present in the clean room air if those having 400 or more molecular weight are used.
As actual examples of (a) and (g), there can be mentioned at least one of microcrystalline wax, natural wax, synthesis paraffin, polyolefin wax, branched alcohol of 18, 20 and 24 carbon number and oleyl alcohol.
As actual examples of (b) and (e), there can be mentioned isononyl phthalate (molecular weight: 418), octyldecyl phthalate (molecular weight: 419), diisodecyl phthalate (molecular weight: 447), lauryl phthalate (molecular weight: 501), myristylyl phthalate (molecular weight: 530), di-2-ethylhexyl azelate (molecular weight: 413), di-2-ethylhexyl sebacate (molecular weight: 427), tris-2-ethylhexyl trimellitate (molecular weight: 547), trioctyl trimellitate (molecular weight: 547), trinonyl trimellitate (molecular weight: 570), tridecyl trimellitate (molecular weight: 612), polyesters obtained by polycondensation of adipic acid, azelaic acid, sebacic acid or phthalic acid and glycol or glycerine (molecular weight: 2,000-8,000), epoxy fatty acid ester (molecular weight: 400-500) and epoxidized oil (molecular weight about 1,000).
As actual examples of (c) and (f), there can be mentioned stearyl-xcex2-(3,5-di-t-butyl-4-hydroxyphenyl) propionate (molecular weight: 520.9), 2,2xe2x80x2-methylene-bis (4-methyl-6-t-butylphenol) (molecular weight: 340.5), 2,2xe2x80x2-methylene-bis (4-ethyl-6-t-butylphenol) (molecular weight 368.54), 4,4xe2x80x2-thiobis (3-methyl-6-t-butylphenol) (molecular weight: 358.5), 4,4xe2x80x2-butylidene-bis (3-methyl-6-t-butyl-phenol) (molecular weight: 382.6), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane (molecular weight: 544.8), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (molecular weight: 775.2), tetrakis (methylene-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl) propionate methane (molecular weight: 1177.7), bis (3,3xe2x80x2--bis (4xe2x80x2-hydroxy-3xe2x80x2-t-butylphenyl) butiric acid) glycol ester (molecular weight: 1177.7) and tocophenol (molecular weight: 794.4).
Further, the present inventors have found that as the molecular weight of the organic substance is greater, the volatility is lowered and the adsorption property is increased, but the adsorption amount to the silicon wafer is decreased and restricted if the molecular weight increases to more than a predetermined amount and that the predetermined amount is different depending on the molecular structure, and definitions for the numerical values in (a)-(c) and (e)-(g) described above were determined based on the result of experiment conducted for a number of targeted materials respectively.
The air filter according to the present invention may be such one as satisfying at least one of the definitions (a)-(c) and (e)-(g) described above, but those satisfying all of them are preferred since no gaseous organic substances are not released from all of the constituent materials of the air filter.
Specifically, preferred are those in which the main ingredient of the non-silicone type water repellent is microcrystalline wax, the main ingredient of the plasticizer contained in the non-silicone series water repellent is tri-2-ethylhexyl trimellitate, the main ingredient of the antioxidant contained in the non-silicone type water repellent is 2,2xe2x80x2-methylene-bis (4-ethyl-6-t-butylphenol), the main ingredient of the plasticizer contained in the sealing material is di-2-ethylhexyl sebacate, the main ingredient of the antioxidant contained in the sealing material is 2,2xe2x80x2-methylene-bis (4-ethyl-6-t-butylphenol) and the main ingredient of the lubricant contained in the sealing material is synthesis paraffin.
Further, the present invention provides an air filter which satisfies at least one of the definitions (a)-(c) and (e)-(d) described above, in which the main ingredient of the sealing material is a two component polyurethane resin formed by reaction between a main agent comprising a polyisocyanate and a curing agent, and the equivalent amount of active hydrogen in the curing agent is more than the equivalent amount of the isocyanate as the main agent and which contains no phosphoric acid ester. In the air filter, since the isocyanates of the main agent do not remain after the curing reaction of the sealing material, isocyanates and diamines caused by reaction of the isocyanate with water in the air are not formed, and since phosphoric acid ester is not released, release of gaseous organic substances from the sealing material is further suppressed.
The present invention further provides an air filter which satisfies at least one of the definitions (a)-(c) and (e)-(g) described above and in which the main ingredient for the sealing material is a two component epoxy resin formed by the reaction between the main ingredient and the curing agent, and the curing agent is acidic or neutral. In the air filter, since a basic amine compound as the curing agent of the sealing material is not contained in the air filter, release of the gaseous organic substances from the sealing material is further suppressed.
The present invention further provides an air filter which satisfies at least one of the definitions (a)-(c) and (e)-(g) described above and in which the main ingredient of the sealing material is a two component epoxy resin formed by the reaction between the main agent and the curing agent is of an amine type and the residual amine is reduced. As the means for reducing the residual amine, there can be mentioned blending and curing such that the amine equivalent is slightly lower than the epoxy equivalent thereby leaving no residual amine after curing, or heating of the resin after curing thereby volatiling the residual amine.
Further, the present invention provides an air filter which satisfies at least one of the definitions (a)-(c) and (e)-(g) described above and in which the filter medium is formed into a cloth-like shape by treating silicone-oil deposited glass fibers with a treatment agent and the silicone oil does not contain cyclosiloxanes having 10 silicon atom or less. Since-cyclosiloxanes having 10 silicon atoms or less are adsorbed extremely easily to the silicon wafer, this filter is suitable, particularly, to an air filter used for a clean room for use in semiconductor production.
Further, the present invention provides a method of manufacturing an air filter including a first step of depositing an silicone oil to glass fibers and a second step of treating the glass fibers with a treatment agent after the first step thereby forming a cloth-like filter medium, which comprises subjecting the glass fibers after the first step to a heat treatment in a clean air stream, thereby sufficiently removing siloxanes having 10 silicon atoms or less from the silicone oil deposited to the glass fibers and then applying a treatment by a treatment agent not releasing gaseous organic substances.
This is one of methods for manufacturing the air filter, in which siloxanes having 10 silicon atoms or less contained in the silicone oil can be removed sufficiently by putting the glass fibers deposited with the silicon oil in a tightly closed vessel and heating, for example, at 120xc2x0 C. for several hours.
Further, the present invention provides a method of manufacturing an air filter including a first step of depositing a silicon oil to glass filters and a second step of treating the glass fibers with a treatment agent, after the first step into a cloth-like filter medium which comprises using those removed with cyclosiloxane having 10 silicon atoms or less as the silicone oil used in the first step and treating them by a treatment agent not forming gaseous organic substances.
This is one of methods for manufacturing the air filter, and siloxanes having 10 silicon atoms or less contained in the silicone oil can be eliminated sufficiently by removing low boiling ingredients by heating, for example, at 200xc2x0 C. in a vacuum state (for example, at vacuum degree of 5 mHg).
Further, the present invention provides a clean room equipped one of air filters each described above.
Further, the present invention provides a local facility equipped with one of air filters each described above. The local facility means, for example, a clean booth disposed to a place where cleanness is intended to be increased locally, or a production facility requiring a predetermined cleanness, for example, a semiconductor production apparatus.
Further, the present invention provides a clean room, in which walls and floors are fabricated with building materials releasing gaseous organic substances in an amount of 50 xcexcg per 1 g or less measured by a purge and trap method, and one of the air filters described above is attached by interposing, between the air filter and an opening used for attachment, a gasket not releasing gaseous organic substances in an amount of 50 xcexcg per 1 g or less measured by the purge and trap method.
When the walls and the floors of the clean room and the gaskets for attaching the air filters are constituted with materials releasing gaseous organic substances in an amount of 50 xcexcg per 1 g or less measured by the purge and trap method, the clean room can be reliably put to a state in which the organic substances are not released in a usual operation state.
If the clean room is used, for example, in a semiconductor production factory, it is possible that the organic substances are scarcely adsorbed to the silicone wafer.
The purge and trap method is a method of passing an inert gas at a predetermined temperature (a temperature at which all the organic ingredients can be volatile) to a predetermined amount of a material, evaporating all the gaseous organic ingredients contained in the specimen, trapping them and quantitatively determining the amount of the gaseous organic substances released from the trapped ingredient.
For the wall materials among the building materials releasing the gaseous organic substances in an amount of 50 xcexcg per 1 g or less, a method of dry sealing a partition system by a fire proof material previously proposed by the present applicant (refer to Patent Laid-Open Sho 62-86248, Utility Model Laid-Open Sho 62-56614 and Utility Model Laid-Open Sho 62-124102) can be adopted and the surface material of the free access floor may be made of inorganic material such as stainless steel for the floor material. The amount of gaseous organic substances released from the wall materials and the floor materials is about 1.0 xcexcg per 1 g.
Further, the present invention provides a treatment agent for impregnation into fibers in order to form the fibers into a cloth-like shape as a filter medium used for the air filter, which satisfies one of the definitions (a)-(c) described above. The treatment agent can suppress the amount of gaseous organic substances released from the air filter manufactured by using them.
As the treatment agent, those satisfying all the definitions (a)-(c) described above are preferred since gaseous organic substances are not released from the main constituent materials.
Further, the present invention provides a method of manufacturing a filter medium which selectively uses those defined with (b), (c) described above as the plasticizer and the antioxidant contained in the treatment agent impregnated in the filter medium. According to this method, a filter medium with less releasing amount of the gaseous organic substances can be manufactured.
The present inventors have further found that the presence of the phosphorus compounds or boron compounds in the clean room is attributable to organic phosphorus compounds (phosphoric esters) contained in the sealing material tightly sealing a portion between the filter medium and the frame of the air filter, and surface material for walls and floors for the phosphorus compounds and attributable to boron oxides contained in glass fibers as the filter medium of the air filter for the boron compounds.
From the findings described above, the present invention provides a clean room in which at least the surface material of the walls and the floors, the filter medium of the air filter and the sealing material for tightly sealing the portion between the filter medium and the frame are formed of such a material as not releasing organic phosphorus compounds and boron compounds into the air.
Further, the present invention provides a clean room in which the material releases gaseous organic phosphor compounds in an amount of 10 xcexcg or less per 1 g of the material by the purge and trap method and leaches boron compounds in an amount of 20 xcexcg or less per 1 g of the material after immersing in ultra-pure water for 28 days.
As described above, even when the constituent materials for the clean room are formed of a material containing the organic phosphorus compounds and the boron compounds, if the amount of the gaseous organic phosphorus compounds released from the constituent material is reduced to 10 xcexcg or less per 1 g by the purge and trap method, and the boron compounds leached after immersion in ultra-pure water for 28 days is reduced to 20 xcexcg or less per 1 g, it is possible that the organic phosphorus compounds and the boron compounds are not present in the clean room air when the clean room is operated in a usual state (at a temperature of 23xc2x0 C., humidity of 30-40% and a flow rate of air passing the air filter of 0.3-0.4 m/s).
Further, the present invention provides a clean room in which the sealing material Is a polyurethane resin type sealing material containing diphenyl methane diisocyanate as a diisocyanate constituting the main ingredient thereof and, when a phosphoric acid ester is contained as a liquefying agent therefor, the molecular weight of the phosphoric acid ester is determined as 300 or more.
In conventional clean rooms, phosphoric acid esters are used as the liquefying agent for the polyurethane resin type sealing material containing diphenyl methane diisocyanate (additive for making diphenyl methane diisocyanate at high purity into a liquid state at a normal temperature) and as a plasticizer or a flame retardant for the vinyl chloride resin type sheet as the surface material for the walls and the floors. Among them, while the carboxylic acid or the like having 400 or more molecular weight shown in (e) described above can be used instead of the phosphoric acid, and aluminum hydroxide, antimony trioxide or the like can be used instead of the phosphoric acid ester for the flame retardant, but there is no substitute for the phosphoric acid ester as the liquefying agent.
Then, If the phosphoric acid ester used is triethyl phosphate (molecular weight 182), tributyl phosphate (molecular weight 266) and tris (xcex2-chloroethyl) phosphate (molecular weight 285) having 300 or less molecular weight, gaseous substances of them are entrained by air passing through the air filter and present in the clean room air in the usual clean rooms described above, but when those having 300 or more molecular weight are used, gaseous substances of them are not present in the clean room air.
Accordingly, it is possible that the phosphoric acid ester is not present the clean room air by using a phosphoric acid ester having 300 or more molecular weight as the liquefying agent and by using the substitute described above or a phosphoric acid ester having 300 or more molecular weight for the plasticizer and the flame retardant.
Further, the present invention provides a clean room in which the phosphoric acid ester used as the liquefying agent is at least one of the substances shown in (h) below. (h) tri-2-ethylhexyl phosphate (molecular weight 435), tributoxyethyl phosphate (molecular weight 398), trioleyl phosphate (molecular weight 849), triphenyl phosphate (molecular weight 326), tricresol phosphate (molecular weight 368), trixylenyl phosphate (molecular weight 410), cresyl phenyl phosphate (molecular weight 340), xylenyl diphenyl phosphate (molecular weight 354), 2-ethylhexyl diphenyl phosphate (molecular weight 362), condensed aromatic phosphoric acid ester (molecular weight not less than 400), trisitridecyl)phosphite (molecular weight 629) and triphenyl phosphite (molecular weight 310).
Further, the present invention provides a local facility in which at least the surface material for the walls, the filter medium for the air filter and the sealing material tightly sealing a portion between the filter medium and the frame are formed of a material not releasing organic phosphorus compounds and boron compounds in the air.
Further, the present invention provides a local facility in which the material releases gaseous organic phosphorus compounds in an amount of 10 xcexcg or less per 1 g of the material by the purge and trap method, and leaches the boron compound in an amount of 20 xcexcg or less per 1 g of the material after immersing in ultra-pure water for 28 days.
Further, the present invention provides a local facility in which the sealing material is a polyurethane resin type sealing material, and contains diphenyl methane diisocyanate as a dlisocyanate constituting the main ingredient thereof and, when the phosphoric acid ester is contained as the liquefying agent therefor, the molecular weight of the phosphoric acid ester is 300 or more.
Further, the present invention provides a local facility in which the phosphoric acid ester used as the liquefying agent is at least one of the substances shown in (h).
As described above also in the local facility, it is possible that the gaseous organic phosphorus compounds or boron compounds are not present in the air at the inside of the local facility by constituting the wall material and the air filter in the same manner as in the case of the clean room.
Accordingly, the clean room and the local facility are particularly suitable to the production of semiconductors.
The air filter according to the present invention is manufactured in the same manner as conventional air filters for use in clean rooms, by treating glass fibers or organic fibers such as of polytetrafluoro ethylene with a treatment agent containing, for example, a binder made, of an acrylic resin or the like, a non-silicone type water repellent, a plasticizer and an antioxidant thereby forming a cloth-like filter medium, putting the filter medium into a frame of a predetermined size and tightly sealing a portion between the frame and the filtration medium with a sealing material, in which those not forming gaseous organic substances during use of the clean room are selected and used as the treatment agent and the sealing material. Specifically, the treatment agent is adapted to satisfy the above definitions (a)-(c), while the sealing material is adapted to satisfy the above definitions (e)-(g).
Further, when the fibers for the filter medium are glass fibers, a silicone oil not containing cyclosiloxanes having 10 silicone atoms or less is used, or glass fibers coated with a silicone oil are subjected to a heat treatment in a clean air stream, to remove cyclosiloxanes having 10 silicon atoms or less, so that cyclosiloxanes having 10 silicone atoms or less are not contained in the filter medium.
Further, in order that the phosphorus compounds and the boron compounds are not present in the clean room and the local facility, at least the surface material for the walls and the floors (only for the walls in the local facility not equipped with floors), the filter medium for the air filter and the sealing material for tightly sealing a portion between the filter medium and the frame are formed of a material not releasing the organic phosphorus compounds and the boron compounds in the air. Specifically, as the materials described above, those releasing gaseous organic phosphorus compounds in an amount of 10 xcexcg or less per 1 g of the material by the purge and trap method and leaching the boron compounds in an amount of 20 xcexcg or less per 1 g of the material after immersing in super-purified water for 28 days are used.